Getting CS8078: An expression is too long or complex to compile after upgrade to Visual Studio 2026

After upgrade to Visual Studio 2026 we are experiencing an issue with some generated source code that compiles successfully when using .NET 10 but when we use the .NET 8 SDK it fails with the following error:

```
Program.cs(15,24,15,27): error CS8078: An expression is too long or complex to compile
```

Our application still targets .NET 8, and we use global.json to specify the SDK requirement like so:
```json
{
"sdk": {
"version": "8.0.416",
"rollForward": "latestFeature"
}
}
```
When building in Visual Studio:
- Target "CoreCompile" in file "C:\Program Files\Microsoft Visual Studio\18\Enterprise\MSBuild\Current\Bin\Roslyn\Microsoft.CSharp.Core.targets"
- Task "Csc" - which uses ...
1> C:\Program Files\Microsoft Visual Studio\\**18\Enterprise\MSBuild\Current\Bin\Roslyn\csc.exe**
- Microsoft (R) Visual C# Compiler version **5.0.0-2.26054.2** (ec501e4c)

**Version Used**:
SDK version 8.0.416 <- uses compiler **5.0.0-2.26054.2** from VS 2026 MSBuild folder as noted above.
SDK version 10.0.101 <- uses compiler **5.0.0-2.25569.105** from dotnet\sdk\10.0.101 folder as noted below.

**Steps to Reproduce**:
I wasn't able to upload the sample code, failed during upload (size limit?) See sample repo here: [https://github.com/JpWebster/VS2026Net8CompileIssue/tree/main]( https://github.com/JpWebster/VS2026Net8CompileIssue/tree/main)
1. Compile the attached source code and get CS8078 error. (Note that this is not our production code but rather some bogus C# code to trigger the CS8078 error so I can test using different csc versions and .NET SDK's)

2. Switch the global.json to use 10.0.101 SDK and the code compiles fine.
```json
{
"sdk": {
"version": "10.0.102",
"rollForward": "latestFeature"
}
}
```
Results in:
- Target "CoreCompile" in file "C:\Program Files\\**dotnet\sdk\10.0.101**\Roslyn\Microsoft.CSharp.Core.targets"
- C:\Program Files\dotnet\sdk\10.0.101\Roslyn\binfx\\..\bincore\csc.exe
- Microsoft (R) Visual C# Compiler version **5.0.0-2.25569.105** (fad253f5)

**Diagnostic Id**:
CS8078: An expression is too long or complex to compile

**Expected Behavior**:
Upgrade to VS 2026 should not break our .NET 8 builds

**Actual Behavior**:
Upgrade to VS 2026 breaks our .NET 8 builds.

We can look to refactor our code to address the issue, however, we'd like to understand what changed in the CSC compiler to cause this error in .NET 8 builds within Visual Studio 2026. Where .NET 10 builds fine in 2026.

I'm not able to determine what recent changes to the compiler may have caused this problem.

Start with the sample repository linked in the issue, especially Program.cs and global.json. Reproduce the build with the .NET 8 SDK under the Visual Studio 2026 Roslyn path, then compare it with the .NET 10 SDK compiler. Done means identifying and documenting the compiler behavior change and a confirmed resolution or disposition for .NET 8 builds.

Written by the indexing model from the issue text.